Television power supply



Sept. 29, 1942,

Patented Sept. 29, 1942 UNlTED STATES PATENT OCFICE TELEVISION POWERSUPPLY Dudley E. Foster, South Orange, N. J., and John A. Rankin, PortWashington, N. Y., assignors to Radio Corporation of America, acorporation of Delaware 1 Claim.

This invention relates to an improvement in television receivers andmore particularly in the power supply used in such receivers.

In a television receiver a cathode ray tube is used in which a beam ofelectrons is generated, the electron beam being directed against afluorescent, luminescent or electron responsive target surface in orderto produce light as a result of the electronic stream bombardment. Theelectron beam is deflected in substantially mutually perpendiculardirections in order to scan the target surface and the intensity of theelectron beam is altered in accordance with the received picture signalseries. The produced variations in the intensity of the cathode raybeam, therefore, together with the scanning operation, produce thetelevision light image at the electron responsive target. The lightimage produced at the target surface may be viewed directly or may beenlarged by projection through a series of lenses upon a viewing screen.

In order to produce a television picture having the desired lightintensity it is necessary to use an electron beam of considerablevelocity and it has been found that velocities and intensities which arenecessary to produce the desired results are suiiicient to permanentlydamage the target surface unless the cathode ray beam is continuouslydeflected. Should the cathode ray beam remain lsubstantially stationaryat any particular point on the target surface permanent injury wouldresult and the surface of the target would be spoiled. Y

The possibility of permanently damaging the target surface of thecathode ray receiving tube is particularly great when the receiver isinitially turned on, since frequently the cathode ray tube and its powersupply are in an operating condition before the deflection generatorsassociated therewith have been sufficiently heated to produce thedesired beam deflections. Under these conditions a cathode ray beam willbe produced and will be directed against a relatively small area on thetarget surface for an appreciable length of time prior to the operationof the deflection generators and as a consequence the target surfacewill be burned over that particular area.

In order to avoid such an operation in conventional receivers, users ofthe receivers have been cautioned to move the beam intensity controlknob to minimum beam position when the receiver is turned on and toleave the control knob in that position for a time suicient for thedeflection generators to begin operation. The

intensity of the cathode ray beam may then be increased by themanipulation of the control knob to a value necessary for properoperation of the tube and receiver. Such a precaution, of course, isannoying to the operator of the receiver and should such a procedure beoverlooked, it is quite possible that the television receiving tubewould be irreparably damaged.

One purpose of the present invention, therefore, resides in animprovement in the power supply associated with the television receivingtube such that production of a cathode ray beam will be prevented for alength of time sufficient to permit the defiection generators to beginoperation.

Another purpose of the present invention resides in the provision ofmeans associated with the power supply of a television receiving tubewhereby the receiver may be turned on without the necessity ofpreviously adjusting the position of the beam intensity control member.

A still further purpose of the present invention resides in theprovision of means associated with the po-wer supply -of a televisionreceiving tube whereby the entire television receiver may be brought toproper operating temperatures and conditions before a cathode ray beamis permitted to be developed in the television receiving tube.

Still other purposes and advantages of the present invention will becomemore apparent to those skilled in the art from the followingspecification, particularly when considered with the single figurewherein a power supply for a television receiver is shown incorporatingthe present invention to accomplish the purposes set forth above.

In the drawing, a television receiving tube I0 is shown having a cathodeI2, a heater element I4 therefor, a screen grid electrode IG, a rstaccelerating anode i8, and a second accelerating anode 20. When properpotentials are applied to these electrodes, a focused cathode ray beamis produced and projected against the target surface 22 at the enlargedend of the television receiving tube IB. For deflecting the cathode raybeam in mutually perpendicular directions dcflecting coils 24 and 26 areprovided which when energized with the proper voltage variations causevertical and horizontal deections of the cathode rai7 beam respectively.Although electromagnetic deflecting means are shown in the drawing, itis to be understood, however, that electrostatic deflection 0r acombination of these types of deiiections may be used. The

to the cathode, the potential being somewhatdess.

than the potential on the second accelerating anode. Furthermore, thescreenfgridelectrode:I6

is maintained positive but1loy-al1lesseramount.as

is well known to those skilled in the-art.

The cathode.,Y ray tube also includes a control electrode 28 by means ofwhichthe vintensityof the cathode ray beam may be controlled and thiscontrol electrode is normally maintained negativel .with respect.to thecathode.l2. In .order .to :modulate the `intensity .of .the cathode ray..beam signals are .applied'asbetween the.. control .electrodeZvand.the..cathode l2. In order to maintain. the; proper. biased.relationship .between the control electrode..and...the cathode ofthecathode `ray tube, the. cathode. may.be..normallyl operated ata.slight .Gand adjustable) .positive .potential withrespectl to.ground..and..thecontrol. electrode 4may. .be operated. at. substantially:ground .potential.

Furthermore, the` potentialoftherst accelerating anodeis adjustable.with respect to the potential .of `the .secondraccelerating anode Yinorder toproduce the. proper-focal. condition ofthe cathode ray beam.

.Forproducing .the desired potentials which L .mustbeapplied..to '..thecathodenay tube, the .power is fappliedto .the terminals 30 which .are.connected to the .primary winding;32..of. thepower transformer' -34..by.way .of=..the. control switchA 36. The power .applied by the terminals30 ,is normally derived. from o the i60 cycle, ..110 .volt commercialsupply system. The .transformer V34 f. has .two .secondary .windings38-and .46, the former-.being for.. the purpose .of .supply-ing .theheating .current tolthe` cathode 42 of thehalf-wave rectifier. tube .44.vThe.other-..secondary.winding 40 which sup- .plieshigh voltageisconnected .between ground and the anode 46 of therectier tube. When .therectifier tubeis energized,..pulsating.direct current may. be. .derivedbetween. cathode 42 `.and thegrounded endl of .the .winding 4.-with theycathode positive ...in .polarity with .respect to ground.

In .order `tot produce Lsubstantially uni-directionalcurrent fromlthepulsating current :a .filter circuit is provided which includescondensers48 and -a. resistance .58. Due .to .the electrostaticcapacityof the condensersfd and. theimpedance .of 'the resista-nce50,.the. potential available. at the output of thelteris. substantiallyconstant. It is' lpossible to. use a. resistance.50` in .place of a.conventional iinductance [choke -inasmuch yas .the .power requiredfto.operate .-.the`. television receiving tube. is relativelyllow,v the.current 'demand being of .the order of -afewmilliamperes .Connectedbetween the output of the .lter supply-and .ground is .aV highresistance..52 which is not .entire1y..necessary..in the..circuit..butwhen -includedassists inimproving the regulation of the rectifier. Theoutput terminal of. thefilter supply is highly. positivewithrespect toground .and this terminal is connected directly .tothe second.accelerating anode. 2G. lIn. order to have available thenecessarypositive., potentials of lowerv inten- .grid electrode is connected tothe junction of resistances 58 and 66, the values of which are so chosenin proportion to the other resistance mem- '.bers.and Lpotentimeters toproduce the desired .potentialfor thescreen grid electrode for nor-Ymal-operation of the cathode ray tube. The cathode-of the'icathoderaytube is connected to the `adjustable -terminal -of the potentimeter 62in order to aord a manual control means for varying-'the averageintensity of the cathode ray beam in orderto .control thebackgroundlevel..of .the

received -television .picture in .a lmanner .Well

known to those skilledin'jthe art.

The drawing also showsa televisiony receiver 64 which includes. meansfor receivngboth the .television.l pictureand sound signals and `.fordevelopingv therefromaudio signals whichare. applied. .to .thespeaker 66:and the detected4 picturesignals which rare. applied between .the-4control electrode 28 an'dcathode. l2 .overrconductorsll The televisionreceiver 64..also :includes deilection generators which .respondto`received synchrOniZingsignals and whichgenerate .voltage variations.necessary to .produce the required.. rate of change of. electromagnetic`v.ux at the .deflection .yoke (includingco'ils- 24.. and-,26) fordeflect- .ingthe cathode raybeamf in mutually perpendicular. directions.The .deflecting coils .24v and.26

.arel therefore. connectedto fthetelevision receiver `(iflby way of.conductors10..and.l2.respectively.

The television receivenshown schematically at 64 also includesapowersupplyfiunit which islnec- .essary to supply the. 4requiredoperati-ng'potentials to thetubes included ;in.the receiver. A'Ihe.-power input of thereceiver-:for thepower .-supplyL contained thereinisthereforeshownas connectedzin .parallel .-with f tha-primary -:32 oftransformer 34 .in 4.order-that the singlecontrol switch. 36- -may.controlthe operationfof the television receiver .aswellastheapplication ofthe-:potentials to the .power -supply v:unit: -for:the` television receiving tube.

With the system as so far described, when the .-powersupply switchv-36is closed=it:.-is-fpessible vfor the 'televisionreceiving tube' yI 0to-beginroperation before `the .-televisionreceiver 64Y has `begun to.operatefand-fasffa consequencethecathode rayf-beam-v. produced in4 thetelevision; receiving vtube-.would .be vdirected againstrthe targetsurface v22^-with considerable 4intensityand velocity before th'edeecting coils24 rand 26 4#would be energized to produce-a dellectionofnthe beam. Such `an -undesirableoperation -could be prevented-asdescribed abovebymanipulationof the beamintens-ity'controljpotentiometer62'so as to increase the bias.onthe-cathode: ray tube :to` a pointfwhere no beam .would'rbeigenerated but,'as stated above, the purpose of the presentinvention istoavoid the necessitytofsuchfa'dnanipulation and toeavoid 1 thepossibilityzof:permanently damaging the .target screenitinthe. absenceofsucha manipulation.

Before acathode Yray Abeam L-canibefgenerated inv a receiving tube,. itis .'-necessaryt .thatf all 'of the' electrodes of the)`gun;structurefhaveapplied thereto approximately the correct operatingpotentials. If, for example, the potential of the first acceleratingelectrode I8 has applied thereto a potential considerably lower thanthat necessary for proper operation of the tube no cathode ray beam willbe produced. In accordance with this invention, therefore, there isprovided a means wherebyr proper operating potentials are not applied toall of the electrodes of the cathode ray tube until after sufficienttime has elapsed to permit the receiver 64 to assume its normaloperating temperature conditions and potentials. In order to prevent theapplication of the correct potentials to the electrodes of the cathoderay tube for a brief period of time immediately following a closure ofthe power supply switch 36 a condenserY 'l5 is provided. This condenseris connected between ground or the negative source of high potential anda point along the potentiometer or voltage divider which is connectedbetween the cathode 42 of the rectifier tube 44 and ground. As shown inthe drawing this condenser l5 is preferably connected between ground andthe junction of resistance 54 and potentiometer 56 so that the screengrid electrode I6 and the rst accelerating electrode I8 are not suppliedwith their proper operating potentials until after the lapse of apredetermined length of time.

The delay in the application of the proper operating potentials to theelectrodes I6 and I8 of the cathode ray tube is a result of the timenecessary for the condenser 15 to be charged through resistance 54 to apotential corresponding to the static potential of the junction pointbetween resistance 54 and potentiometer 56. When th'e televisionreceiving set is in an inoperative condition (switch 36 open) thecondenser 15 will have no charge thereon since any previous existingcharge will be dissipated through resistclosure of switch 36 a certainrather bri-ef time delay is necessary to permit electrons to ow throughthe rectier tube. After the expiration of this time, however, therectier tube will operate and a positive potential will appear at theoutput end of the filter resistance 50. Since the I' condenser l5 isrelatively large and inasmuch' as the resistance 54 is quite high, thejunction of the resistance 54 and the potentiometer 56 will be atsubstantially ground potential and the potential of this point willincrease in a positive direction at a relatively slow rate. During thistime no cathode ray beam can be produced in the television receivingtube since the condenser 'l5 prevents normal application of properoperating potentials to the electrodes I6 and I8. After the elapse of apredetermined time interval, as determined by the size of the resistance54 and the capacity of the condenser 15, a cathode ray beam will beproduced but by this time the television receiver 64 will have reachedproper operating condition and deflection energy will be present in thedeflecting coils 24 and 26. Accordingly, through the use of condenser l5it is possible to turn on the television receiving set without thenecessity of first adjusting the background control potentiometer 62 andwithout any possibility of the production of a cathode ray beam in thereceiving beam prior to normal operation of the television receiver 64.

Since the amount of current required to operate the television receivingtube i6 is relatively low, the aggregate resistance of the voltagedivider connected across the high voltage power supply may be quitehigh. rIhe total resistance included in the voltage divider is normallychosen such that the current ow therethrough will be of the order of oneor two milliamperes. Furthermore, since the voltage applied to the firstaccelerating anode I8 is of the order of onethird to one-sixth of thepotential applied to the second accelerating anode 26, the value of theresistance 54 is quite high and materially in excess of the combinedresistance of the remaining elements of the voltage divider. In view ofthe fact that a very high resistance is included between the ungroundedplate of the condenser 15 and the positive terminal of the power supply,the charging rate of the condenser 'l5 is relatively slow and the sizeof the condenser 15 need not be particularly large and may well be of avalue which can be conveniently and economically included in atelevision receiver. As stated above. the size of the condenser l5determines the time which must expire before proper operating potentialsare applied to the electrodes of the cathode ray tube and accordinglythe condenser 15 is chosen in accordance with the length of time that itis desired to prevent production of the cathode ray beam. This timeinterval should, of course, considerably exceed the length of timerequired for the television receiver 64 to begin full operation.

From the above, it may be seen, therefore, that a new and improved powersupply for a television receiver has been developed wherein anypossibility of permanently damaging the target electrode in a televisionreceiving tube by reason of a delay in the operation of the televisionreceiver has been substantially entirely eliminated. Furthermore, it maybe seen that through the exercise of the present invention, such asafeguard can be very conveniently and economically included in atelevision receiver.

It should be understood that the present invention is applicable toeither a direct viewing tube or to a projection tube and although a tubeof the direct viewing type is shown in the drawing, it is very desirableto apply the described invention to projection tubes since the beamvelocities of such tubes and the intensity of the cathode ray beam arerelatively high and consequently the target screen could be permanentlyruined in a very short space of time.

Various alterations and modifications of the present invention maybecome apparent to those skilled in the art and it is desirable that anyand all such modifications and alterations be considered within theperview of the present invention except as limited by the hereinafterappended claim.

We claim:

.A power supply for a television receiver including a rectifier and afilter network for supplying a source of direct current potential. avoltage divider connected across said source of potential including aplurality of resistor elements, a cathode ray tube including a cathode,a first accelerating anode and a second accelerating anode` means forconnecting said second accelerating anode to the positive potential endof idlhe voltage divider, .meansifor connecting ,the frst :accelerating:anode to one of :the vresistor elementsi of the fvoltag'e f dividermeans Vfor connecting the cathode tohthevoltagetdvider near -thenegative endthereof.; and aondenser directly y*connected between `thenegative end of the voltage dividerandafpoint along the voltage ydividernear rwhere the rst, accelerating anode fisfgconnected -Wherebyrwhen-a,source of potential anode will; gradually increasein; ya.positivefzdirecytion :at a ratei determinedgbyjthefsize ffofithe`condenser ;and the; resistance of 1 the'yoltage divider through lwhichit js-A charged.

.DUDLEY rE. ,-FOS'PER. JOHN A.:RANKIN.

